Distribution of organic carbon in the Luochuan loess/paleosol and its relationship with clay minerals

The total organic carbon (TOC) and its major components, i.e., stable organic carbon (StOC), mineral-protected organic carbon (MOC), and chemical resistant organic carbon (COC), were analyzed for both loess and paleosol layers in Luochuan profile, and the correlations between the clay particle content, clay mineral content and TOC content were studied. The results are as follows: (1) the content of TOC is higher in paleosol (except for S ₄) than in loess, but the differences of the average content of StOC, MOC, COC are not obvious between loess and paleosol; (2) the loess and paleosol needed different time spans to reach the stabilization of the values of TOC: the former needed about 140~250 ka and the latter needed 330~410 ka; (3) the clay particle content is well correlated with TOC content and COC content (r=0.46, r=0.54), whereas the slit content and the fine sand particle content are poorly corrected with TOC content and COC content. The results indicate that the clay particle is a significant composition for storage of carbon organic in soils; (4) kaolinite content is highly correlated with TOC content and COC content (r=0.74, r=0.61), whereas illite and montmorillonite are not correlated or poorly correlated with TOC content and COC content.